[NAIROBI] Parasites that cause leishmaniasis — a neglected tropical disease transmitted by sand flies — could adopt a dormant phase that might render them invisible to drugs and the host’s immune system, a study suggests.

According to the WHO, about 50,000 to 90,000 new cases of the most serious form of the disease, called visceral leishmaniasis or kala-azar, occur globally a year. Of the new cases of kala-azar the WHO received in 2015, 90 per cent came from seven nations: Brazil, Ethiopia, India, Kenya, Somalia, South Sudan and Sudan.

“There is a need to recognise the disease’s existence and incorporate it into ministries of health’s strategic plans.”

Bashir Mwambi

The study published in PLOS One journal on 25 July by researchers from Belgium, Peru and the United States shows that the parasites causing leishmaniasis are capable of surviving in a dormant state up to seven days and even more.

Co-author Jean-Claude Dujardin, a biologist and head of the Department of Biomedical Sciences at the Instutute of Tropical Medicine Antwerp, Belgium, says they compared the parasite Leishmania braziliensis in the proliferative form called amastigote encountered in the sand fly and in the form encountered in a mammalian host: mice.

They then characterised some key biological processes and discovered that the whole protein synthesis machinery was shut down and that the parasite was living in an economic energy consumption mode.

Few drugs are available to treat this deadly and mutilating disease and several of these have lost or are losing their efficacy, says Dujardin, adding that affected people are often poor. “This makes the development of new drugs a non-profitable activity for pharmaceutical companies,” he explains.

Marlene Jara, a co-author and a doctoral student at the Universidad Peruana Cayetano Heredia, Lima, Peru and the Instutute of Tropical Medicine Antwerp, tells SciDev.Net that the parasite remains dormant to ensure its survival over long periods. “It can be due to drug resistance, meaning the parasite has acquired a mutation which allows it, for instance, to pump out the drug, but we observe many cases in which treatment does not function in the absence of drug resistance,” Jara explains. “But the environmental conditions and the molecular mechanism that trigger this process are not completely understood yet.”

According to Bashir Mwambi, a microbiologist and a lecturer at the Uganda-based International Health Sciences University, the parasite remaining dormant threatens its management, adding that the study suggests that even areas originally pronounced free of leishmaniasis probably are not entirely free, and that continuous transmission is possible.

Mwambi calls for emphasis on preventive methods including mass education, the need for screening of blood for transfusion for leishmaniasis, and increased researchfunding, especially in drug susceptibility tests to establish whether drug resistance is not responsible for those who have the disease.